Final Exam /415 ( CHEM 6352 Fall %) Name

Transcription

1 Final Exam /415 ( CEM 6352 Fall 2011 %) Name Dec. 15 th, :00-12:00 You may NT use any references or aids to complete the following with the exception of a chemical model set and the scrap paper that I provide at the end of the test. Note that showing proper stereochemistry and the rational for that stereochemistry will be graded. ALWAYS show a rationale for new stereochemistry (including substituted olefins) if a reaction would be selective. Also note that chiral structures with designated stereochemistry (i.e. hashes and wedges) are assumed to be enantiopure unless a racemic mixture is explicitly stated. You may use existing structures in the problems for your rational if appropriate. <<BNUS items are optional but worth additional points.>> (25 bonus points) Note that the following compounds can be used for any problem on the test. All other reagents you use may incorporate in the reaction product only 4 carbons or less in a given reaction. C 6 13 BnBr CEM 6352 Library Si Cl Grubb's Catalyst C 2 i-pr N B Bu N Cl Br Bu 4 NF TMS Li B C 2 i-pr MPU N 9-BBN Me Et N Ac Ac I Ac I i-pr 2 C i-pr 2 C B TMS Et 3 N Cp C Me Ti Al Cp Cl Me B Bu 2 N (Et) 2 P()CC 2 Et Bu 2 BTf B TMS

2 1. Predict the major products and any new stereochemistry found therein. A. (10 points) Kt-Bu, t-bu <<BNUS (5 points): What Baldwin s rules classification(s) would used for bond formation here?>> B. (10 points) 1) CBr 4, P 3, Zn 2) nbuli (2 equiv) 3) aqueous workup C. (10 points) N 2 P Et Et <<BNUS (10 points): provide a mechanism for this transformation.>>

3 D. (10 points) CN Kt-Bu E. (10 points) CN Kt-Bu F. (10 points) h!

4 2. Provide reagents for these transformations. A. (5 points) NMe 2 NMe 2 B. (5 points) NMe 2 NMe 2 C. (5 points) NMe 2 NMe 2

5 D. (10 points) Br E. (10 points) Me Me 3. Pick your favorite name reaction! Provide the name of the reaction and an example of the overall transformation. Also, state why you think it is useful. (15 points)

6 4. Describe a synthesis of the compounds on the left from the starting materials on the right. Use reagents from the CEM 6352 library or that add 4 carbons or less. A. (15 points) B. (5 points)

7 C. (5 points) 5. Draw a mechanism for the following reaction. (10 points) N 2 N 2 Me 65 C N N

8 6. A. Predict the major product for the following reaction and provide a detailed explanation of the chemoselectivity, regioselectivity, and diastereoselectivity involved. (20 points) TMS Me 1) Me 2 AlCl (1.1 equiv) Me C 2 Cl 2, -40 C 2) LiB 4 3) 3 + A B B. Propose a strategy and reagents to make this reaction enantioselective and provide product B as one enantiomer. (10 points)

9 C. Using the enantiopure B made above, propose reagents to provide the final product shown below as one enantiomer. Give a reason for stereoselectivity. (10 points) Me B 7. John Soderquist spoke to use about the allyl borane shown below. We also mentioned it in lecture. Show the transition state for this reagent reacting with the indicated aldehyde. Then, show the expected product for the reaction. (15 points) B TMS 2 workup

10 8. The following reactions would NT give the indicated product. State WY NT. Predict the actual outcome of the reaction. A. (10 points) LDA; BnBr ne Enantiomer! ne Enantiomer! B. (5 points) NaMe Br Me C. (10 points) Br heat Br (±)

11 D. (5 points) N (Bu) 2 BTf Et 3 N N E. (15 points) mcpba

12 9. Propose two different enantioselective syntheses for the following two molecules using substantially different strategies. A. (30 points) Bn S S Me S S ne Enantiomer! Approach #1: Approach #2:

13 B. (30 points) Bn S S Me S S ne Enantiomer! Approach #1: Approach #2:

14 10.Below is the entire synthetic sequence for Danishefsky s approach to (+)-Estrone. A. Provide structures for synthetic intermediates of the sequence in the boxes provided. (25 points) 1) Et 3 N 1) 2, Pd/C N 2) L-phenyl alanine, Cl 4 3) NaB 4 2) (C 2 ) 2, + 1) Li, N 3 (l) 2) Na then + 1) Cr 3, 2 S 4 2) pts, Ac 1) AcBr, Ac 2 2) K 2 C 3, Me (+)-Estrone

15 B. Provide a mechanism for the Birch reduction/base/acid to form the enone shown below. You may abbreviate any unchanging portions of the compound as R groups. (10 points) 1) Li, N 3 (l) 2) Na then +

16 11. Propose an ENANTISELECTIVE synthesis for each of the following molecules. (25 points each) A. ne Enantiomer!

17 B. ne Enantiomer!

18 C. ne Enantiomer!

19 <<12. BNUS (10 points): Give an example of a new discovery that has appeared in the chemical literature during this semester. For full points you should include the name of the author and journal in which it appeared.>>